Adenosine is a potent regulator of brain function. Accumulation of adenosine activates the adenosine receptor A2A-R, which modulates neuronal activity. Expression of A2A-R is high in certain types of neurons, but low in astrocytes. We found that expression of A2A-R is abnormally high in astrocytes in patients with Alzheimer's disease (AD) and in an AD mouse model. A2A-R levels in postmortem human brains strongly correlated with the levels of AD pathology. Based on these unexpected results, we hypothesize that astrocytic A2A-R is involved in AD pathogenesis. To test our hypothesis, we will examine AD-related cognitive dysfunction in mice after manipulating astrocytic A2A-R expression levels. We will also investigate the mechanisms by which astrocytic A2A-R may influence neuronal function. A2A-R signals through the intracellular Gs-coupled pathway and has been implicated in retraction of astrocytic processes, which are lost in postmortem AD brain and AD mouse models. Indeed, both adenosine and activators of Gs-coupled signaling induce process retraction in cultured astrocytes. Notably, astrocyte retraction is linked to changes in neuronal function. However, few studies have addressed the causes of astrocytic retraction or its possible role in AD-related neuronal dysfunction. We will determine whether Gs-coupled signaling by A2A-R triggers retraction in astrocytes and alters neuronal activity. In summary, we propose to examine whether elevated levels of A2A-R, through intracellular Gs-coupled signaling, induce aberrant astrocytic retraction and contribute to AD-related neuronal dysfunction. Investigating this novel astrocyte-neuron interaction may uncover new roles for astrocytes and adenosine receptors in AD and offer new therapeutic targets for alleviating AD-related cognitive decline. These studies may also reveal a novel mechanism by which astrocytes regulate neuronal activity and contribute to normal brain function. The proposed aims and experimental approaches are driven by the working hypothesis that adenosine activates astrocytic A2A-R and leads to Gs-coupled intracellular signaling, which induces morphological changes in astrocytes and downstream changes in neuronal activity. Diverse techniques will be used to test this working hypothesis, including behavioral assessment in mice, live time-lapse confocal imaging, and electrophysiology. Alternative strategies are outlined to ensure success in the event of technical difficulties with particularly challenging experiments. The proposed research promises to enhance our understanding of normal brain function and may pave the path towards an effective strategy for the prevention or treatment of AD. The research plan will also provide a rigorous scientific training opportunity for the candidate in the fields of neurodegeneration and glial-neuronal interactions.